This 5.1 MHz circuit was found in a 1980s documentation. The frequency is given by the crystal and general purpose transistors can be used.
This is the circuit of a “follow the line” type robot with inductive sensors published in Radio...
With a unijunction transistor and a tunnel diode it is possible to obtain rise times of 1 ns with...
This receiver for listening to headphones and 2-battery power was found in Japanese documentation from the...